γ-Glutamyl-valyl-glycine (γ-Glu-Val-Gly) has been known as a peptide giving rich flavor to food (Patent Literature 1). γ-Glutamyl-valyl-glycine is, for example, produced by chemical synthesis methods or enzymatic methods. Among them, when γ-glutamyl-valyl-glycine is produced by enzymatic methods, for example, valyl-glycine or a salt thereof is reacted with a glutamyl group donor, such as glutamine, in the presence of γ-glutamyl transferase (hereinafter, γ-glutamyl transferase is also referred to as “GGT”) to produce a solution containing γ-glutamyl-valyl-glycine, and then γ-glutamyl-valyl-glycine is obtained from the solution (Non Patent Literature 1).